The Land Rover is - undeniably - a great vehicle. However, I liked the Unimog capabilities
"Unimogs can be equipped with front and rear tool mounting brackets and hydraulic connections to allow bucket loaders and hydraulic arms to be used. Most units have a power takeoff (PTO) connection to operate rotary equipment such as snow brooms, snow blowers, brush mowers, or stationary conveyor belts."
"They can be equipped with a backhoe, front loader, or other contracting equipment. On railroads, Unimogs are used as rail car movers and road-rail vehicles. "
(Both quotes from Wikipedia)
I also like the Unimog's carrying/towing capacity (both higher than the Land Rover) although I might go for the Mercedes G-Wagen as an equivalent to the XR-311
Also, please note, that the AP planners don't expect to find spares for any vehicle. The Atlantis Project was set up for the "wake up after 150-years" scenario